Table 2.

Studies reporting inhibitory activity of natural flavonoids against human coronavirus proteins.

Viral proteins	Compounds	Effects	Methods	Reference
SARS-CoV PLpro	Geranylated flavonoids (tomentin A-E)	IC50 = 5.0–14.4 μM	fluorogenic peptide Z-RLRGG-AMC	[54]
SARS-CoV PLpro	Bavachinin	IC50 = 4.2–38.4 μM	fluorogenic peptide Z-RLRGG-AMC	[53]
	Corylifol A Isobavachalcone
	4′-O-methylbavachalcone
	Neobavaisoflavone
	Psoralidin
SARS-CoV PLpro	Papyriflavonol A	IC50 = 3.7 μM	fluorogenic peptide Z-RLRGG-AMC	[55]
SARS-CoV PLpro	Xanthoangelol E	IC50 = 1.2 μM	cell-free method	[58]
SARS-CoV 3CLpro	Xanthoangelol E	IC50 = 11.4 μM	cell-free method	[58]
		IC50 = 7.1 μM	cell-based method
SARS-CoV 3CLpro	Herbacetin	IC50 = 33.17	recombinant protein; FRET method	[57]
	Pectolinarin	IC50 = 27.45
	Rhoifolin	IC50 = 37.78 μM
SARS-CoV 3CLpro	Isatis indigotica extract	IC50 = 53.8 μg/ml	cell-free method	[49]
	Hesperetin	IC50 = 60 μM
SARS-CoV 3CLpro	Quercetin-3-β-galactoside	IC50 = 42.79 μM	recombinant protein	[50]
SARS-CoV 3CLpro	Amentoflavone	IC50 = 8.3 μM	recombinant protein; FRET method	[51]
SARS-CoV 3CLpro	Epigallocatechin gallate	IC50 = 47–73 μM.	recombinant protein; FRET method	[52]
	Gallocatechin gallate
	Quercetin
MERS-CoV 3CLpro	Helichrysetin	IC50 = 40.59 μM	recombinant protein FRET method	[56]
	Herbacetin	IC50 = 35.85 μM
	Isobavachalcone	IC50 = 37.03 μM
	Quercetin 3‐β‐D‐glucoside	IC50 = 67.04 μM
SARS-CoV NTPase/helicase	Quercetin	IC50 = 8.1 μM	recombinant protein FRET-based dsDNA unwinding assay	[62]
SARS-CoV NTPase/helicase	7-O-arylmethylquercetin derivatives	IC50 = 2.7–5.2 μM	recombinant protein FRET-based dsDNA unwinding assay	[63]
SARS-CoV NTPase/helicase	Myricetin	IC50 = 2.71 μM	recombinant protein FRET-based dsDNA unwinding assay	[64]
ATPase activity	Scutellarein	IC50 = 0.86 μM	ATP hydrolysis colorimetric assay
N protein	Catechin gallate	0.05 μg/ml (40% inhibition)	quantum dots (QDs)-conjugated RNA oligonucleotide on biochip	[60]
	Gallocatechin gallate